During maintenance of aircraft and other industrial equipment, it is often necessary to remove previously installed blind rivets, blind bolts, and similar fasteners. This is generally a difficult, multi-step process. All rivets and similar rivet-like fasteners have, at a minimum, a sleeve, or rivet body, and a stem which upsets the blind side of the sleeve when the stem is pulled with sufficient force during installation, so the rivet holds at least two work pieces together. Removal of a rivet involves drilling though one or more parts of the rivet. Aerospace fasteners are more sophisticated and usually include locking rings or other locking devices that add further difficulty to the rivet removal process. Aluminum rivets are fairly easy to drill into and remove, but aerospace fasteners currently in use are made of alloy metals, stainless steel, Monel®, Inconel®, and the like, which are extremely difficult to remove after being initially installed. These alloy steel fasteners are difficult to drill, and those with locking rings that hold the rivet stems in place once they have been upset (pulled) by the installation tool are harder still to drill, in addition to adding at least one extra drilling step for removal.
Rivet removal involves a number of steps, and there are about as many techniques for fastener removal as there are artisans doing them. It has never been an easy process. The two leading fastener manufacturers, Cherry Aerospace and Huck (Alcoa Fastening Systems) each have a process manual for fastener removal, and Huck even produces tooling for rivet removal. However, no process in use until now has been fool proof. An example of a rivet removal process is taken from instructions provided at www.alcoa.com. As illustrated in FIG. 1, a rivet has a sleeve 10 with a head 12 and a locking ring 14 (the first feature below the top surface of the rivet head 12), and a stem 16, joining work pieces 18 and 20. With the stem 16 in place, the rivet is, by design, doing what it is supposed to do, holding work pieces together.                Step 1, FIG. 1a: A small center drill bit 22 is used to provide a guide for a larger drill.        Step 2, FIG. 1b: A high strength drill bit 24 of a diameter equal to the diameter of rivet stem 16 is used to drill to depth of locking ring 14. If there is a locking ring or collar in place, such as locking ring 14, it must be drilled out so the stem 16 is free to be punched out of the rivet sleeve 10 in step 2.        Step 3, FIG. 1c: A steel drift pin 26 of proper size is used to drive out the rivet stem 16.        Step 4, FIG. 1d: A drill bit 28 having the same diameter as the outer diameter of rivet sleeve 10 is used to drill nearly through the rivet head 12.        Step 5, FIG. 1e: A drift pin 30 is used as a pry to break off rivet head 12.        Step 6, FIG. 1f: A drift pin 32 having the same outer diameter as the rivet sleeve 10 is used to drive the sleeve out.        
Most rivets are designed to clamp together the two work pieces they are installed into, but they may not be designed to fully fill the holes they are installed through and may not have good “hole fill” characteristics. This is particularly true for rivets used in composite structures in both aircraft and industrial applications. Some rivets are designed to both clamp the work pieces together and fill the hole at the same time; they have both “clamp up” and “hole fill” characteristics. Thus, if the rivet is of the “clamp up” design only, which most are, the sleeve is easily caused to spin when drilled during steps 1 and 2, and especially in step 4 after the stem is removed, due to the partial release of the “clamp up” force with removal of the stem. A drill bit turns in a clockwise direction and causes the rivet sleeve to rotate in the same direction if the torque applied to the rivet sleeve by the drill exceeds the “clamp up” force that was established when the rivet was installed into the work pieces. Therefore, the problem is most severe with rivets that clamp the pieces together without “hole fill” capability, but also encountered with rivets that do have “hole fill” characteristics. Wire draw rivets have sleeves that are designed expand and fill the hole during installation. So, it is simply a matter of physics: if the torque load of the drill bit during the rivet removal process exceeds the applied “clamp up” and “hole fill” forces of the installed fastener, the rivet sleeve will spin. If a rivet spins during the removal process, it can damage the work piece or airframe component and become nearly impossible to remove other than by grinding off the rivet head. Grinding metal alloy rivets can easily damage the work piece if the artisan is not careful. In the case of a composite airframe component, the heat buildup from grinding will indeed damage the resins in the composite material, which will require complete replacement of the component, a process that is expensive and will require the removal of numerous other fasteners.
Thus, there is a need for a system and method for removing previously installed blind rivets and similar fasteners reliably and more simply than can be done with current tools and methods.